Writing instrument



FIG. 1 is a rear elevational view thereof;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a right side elevational thereof; the left side elevational view being a mirror image thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a writing instrument, as shown and described. 